Robots supporting body parts of elderly people growing due to an aging society and persons who acquired disability due to various accidents have been introduced.
Such devices supporting movement of those with impaired mobility have been continuously developed and commercialized. A leg-supporting robot supporting movement of a malfunctioning leg is a representative example of such devices.
The leg-supporting robot is a robot which provides joint torque to support weak legs of the disabled, the wounded, or the elderly when walking erect so that they may walk like normal people. Generally, an electric motor is used to provide the joint torque of the leg-supporting robot.
Since the leg-supporting robot is a robot designed to be worn by a user, an electric motor used therein should be manufactured to be small in size to reduce the weight and volume of the robot. Furthermore, a speed reducer is used in the electric motor to secure output torque.
However, when the speed reducer is used in the electric motor, the output torque of the electric motor increases according to a gear ratio but a degree of mechanical friction that a user may feel is not low due to a friction force generated when a plurality of gears are rotated while being engaged with each other.
Due to the mechanical force generated by the plurality of gears, the user would feel the sense of irritation and discomfort when the user wears the leg-supporting robot.
That is, during use of the leg-supporting robot, driving power for joints is provided by torque generated by the electric motor when walking erect but a user who wants to move a joint slightly or change his or her posture would feel, from the leg-supporting robot, a large degree of friction force interrupting the movement of the joint according to the user's intention when the driving power is not needed.
Accordingly, the mechanical friction of the leg-supporting robot should be reduced to actuate the leg-supporting robot according to a situation of a user who wears it and guarantee the user's flexible movement. However, although providing a sufficient degree of driving power for joints and reducing the mechanical friction to secure the user's flexible movement are contrary to each other in terms of purpose or function, there should be a trade-off between them.